The goal is to develop a reliable teratogen prescreen test employing embryos of the sea urchin, Strongylocentrotus purpuratus. A sea urchin embryo screen would complement existing tests designed to prioritize potential teratogens at a relatively low cost. The approach involves testing for mortality and structural abnormalities induced by chemical exposure during the embryonic development of the larval organism. Toxicity of the chemical administered in an identical manner to a later larval stage, the pluteus larva, would permit a direct comparison between the concentration of chemical causing teratogenic effects (in the embryo) associated with unique embryological processes, and the concentration resulting in frank toxicity to an organism (the pluteus larva) not undergoing tissue differentiation and organogenisis with respect to larval structures and function. Phase I studies will concentrate on protocol development, including the selection of effects criteria, and initial evaluation of the experimental design. Then a select series of teratogens and non-teratogens, about 20 compounds in all, will be examined using the method to evaluate its feasibility. If the phase I studies are promising, then phase II will refine the protocol, substantially enlarge the documentation data base (of chemicals tested), and attempt to incorporate automation into the test. A reliable test will have commercial potential as a teratogen test service, and possibly for the manufacture of a partially automated test system.